1. The Field of the Invention
The present invention is related to a tool for extracting threaded inserts from threaded holes. More particularly, the present invention is related to a tool which is capable of cutting at least one groove in the interior surface of a threaded insert and then applying torque to the edge of the groove to twist the insert out of a threaded hole without risk of damage to the parent threads.
2. Technical Background
Threaded inserts are commonly used in the repair and refurbishing of mechanical mechanisms. In many situations it is common for threaded holes to be damaged such that the threads are no longer in their original usable condition. For example, it is common for a bolt placed within a threaded hole to become lodged. Removal of the bolt may require the application of forces sufficient to damage the threads within the threaded hole. Alternatively, simple wear and tear may eventually result in such damage to the threads within a hole that they will no longer satisfactorily perform their intended functions.
Once a set of threads is damaged, however, there are a limited number of steps that can be taken in order to reuse or replace the mechanical part which includes a threaded hole. One alternative is to discard the part. This alternative is only practical, however, when the part is relatively inexpensive and replacement parts are readily available. In the case of damaged threads included on large, complex, or expensive pieces of machinery, it may not be practical to simply replace the part. Rather, refurbishment of the part may be required.
One method of partially repairing damaged threads involves drilling out the damaged threads and then re-threading the new larger hole. It is obvious, however, that the new hole will no longer be capable of holding a bolt of the same size as the original hole. In order to solve this problem, it is conventional to insert a threaded insert, such as those sold under the Helicoil.RTM. tradename, into the newly threaded hole.
A threaded insert is essentially a coiled helix. Such a device is a coiled strand, shaped in the same general manner as a coiled spring. The strand may be a rhombus or some other shape in cross-section. The insert is inserted into the newly threaded hole by first winding or compressing the coil in the same manner that a coil spring would be wound. Specialized tools are commercially available for winding a threaded insert for insertion. The diameter of the coil is reduced during the winding step, providing for easy insertion of the coil into the threaded hole. When the insertion tool is removed, the coil unwinds and expands, seating the coil into the parent threads. Thus, the coil engages the parent threads through friction.
Once the threaded insert is secured in place, it is possible to insert a bolt of the same size previously used in the device because the gap between the bolt and the parent threads is filled by the threaded insert. Thus, it is not necessary to replace the device having the damaged threads, or to resort to a larger sized bolt. As mentioned above, this mechanism is used in many different contexts, from small engines to very large and complex machinery.
Threaded inserts are commonly used in connection with aluminum. Because of its light weight compared to steel and many other metals, aluminum is a favored material for the construction of aircraft components and other parts employed in weight-sensitive contexts. However, aluminum is not as strong as heavier metals. Consequently, torque values which may be maintained in aluminum threads are necessarily limited. By utilizing a threaded insert, the parent threads may be bigger, thereby enhancing the torque per surface area ratio and resulting in stronger attachment of the bolt to the threads.
One problem that has been frequently encountered in the use of threaded inserts is the difficulty in removal of the inserts from the threaded holes after insertion. It is often necessary, over the life of a piece of machinery, to remove and replace the threaded inserts. Refurbishment of space shuttle booster motors, for instance, requires the removal of hundreds of threaded inserts; the nozzle assembly alone includes over 1500 holes in which threaded inserts are utilized. Reasons for removal may include corrosion between the insert and the parent threads, damage to the threaded insert during use, or a need to fully refurbish the mechanical part in which the insert is seated.
It is conventional in the art to remove threaded inserts by using a standard wedge-shaped extraction tool, such as that disclosed in U.S. Pat. No. 2,244,824 to H. Caminez. Such an extraction tool is wedged down into the interior of the threaded hole until it engages the threaded insert. The wedge is generally provided with sharpened edges which are driven into the inside diameter of the first coil of the threaded insert. Once the tool has engaged the coil, the tool is twisted in the appropriate direction to back the insert out of the parent threads.
It will be appreciated that this type of tool has serious drawbacks in extracting threaded inserts. One drawback relates to the forces which are exerted on the insert. In order for the wedge to securely maintain engagement with the insert during extraction, the wedge must continuously be forced toward the bottom of the hole. Because the wedge is triangular, forcing the wedge toward the bottom of the hole also forces the threaded insert outward against the parent threads. This outward force in turn increases the friction between the insert and the parent threads, making it harder to remove the insert. The outward force may also damage the parent threads.
Another disadvantage of the prior art wedge-shaped tool is apparent when the first thread of the insert lies appreciably below the top of the hole. In this situation, the wedge may directly engage and damage the parent threads. The hole must then be drilled out, rethreaded, and fitted with two threaded inserts instead of one to permit continued use of bolts of a given diameter. Use of a second insert in this manner may be unacceptable due to the time required, the proximity of other holes to the damaged hole, or other engineering constraints.
Yet another drawback of the wedge tool is the lack of any structure to align the tool with respect to the hole. Misalignment may permit one blade of the wedge to cut completely through the threaded insert and damage the parent threads when pressure is applied to the tool to secure it in engagement with the threaded insert.
A further drawback of the wedge tool is the tendency of the tool to induce carpal tunnel syndrome or similar ailments in workers who repeatedly employ the tool to remove threaded inserts. The top of the tool is fitted with a T-shaped handle, rather than a hex-shaped head or other configuration suitable for engaging the tool to a drive mechanism such as a ratchet or a motor. Moreover, even if a drive mechanism were attached, workers would still be required to manually maintain alignment, since the wedge tool lacks any structure to align the tool to protect the parent threads.
An additional drawback of prior art devices arises from the fact that many applications employ a flange above the hole. The flange prevents the user from visually determining whether there is a threaded insert in the hole. If the wedge tool is inserted in a hole that contains no insert, the wedge blades may engage and damage the parent threads before the leading tip of the wedge reaches the bottom of the hole. The tool of this invention, by contrast, permits a tactile determination of whether an insert is present without engaging the grooving edge of the blades against the parent threads.
Thus, it would be an advancement in the art to provide a tool for extraction of threaded inserts which overcomes the drawbacks of existing extraction tools. More particularly, it would be an advancement in the art to provide a threaded insert extraction tool which is capable of extracting inserts without the necessity of wedging the tool into the interior of the insert. Such an advancement would reduce both the risk of damage to the parent threads and the friction between the insert and the parent threads that opposes extraction.
It would also be an advancement in the art to provide such a removal tool which is capable of extracting threaded inserts positioned at various distances below the top of the hole without risking damage to the parent threads.
It would be an additional advancement to provide a tool whose blades are maintained in alignment with the hole, thereby reducing the danger of destroying the parent threads.
It would be a further advancement in the art to reduce the risk of carpal tunnel syndrome and similar ailments in workers by providing a threaded insert removal tool suitable for use with a drive mechanism.
It would also be an advancement to provide a threaded insert tool configured to permit a tactile determination of the presence or absence of an insert without significant risk to the parent threads of empty holes.
Such an apparatus is disclosed and claimed herein.